A barrier film in which a thin layer of a metal oxide such as aluminum oxide, magnesium oxide, or silicon oxide is formed on the surface of a plastic substrate or a film has been widely used for packaging a product which requires blocking of various types of gases such as water vapor and oxygen or for packaging to prevent the quality change of, for example, food, industrial products or medical products. Also, aside from the use for packaging, a barrier films has been used as a substrate for a liquid crystal display, solar cell, organic electroluminescence (EL) and the like.
An aluminum foil has been widely used as a packaging material in this field, however, disposal after use is becoming a problem, and, in addition, since an aluminum foil is basically an opaque material, it has a problem that it is difficult to check the content from outside. Further, it is absolutely difficult to be used for a display material which requires transparency.
Specifically, for a transparent substrate of which application to a liquid crystal display or a solar cell is in progress, added has been higher level of requirements, for example, capability of roll to roll production of the substrate, durability for a long period, freedom of the shape, and capability of curved display, in addition to the requirements of weight saving and getting larger. Replacement of a glass substrate which is heavy, fragile and difficult in increasing the size to a film substrate such as a transparent plastic is also in progress. For example, application of a polymer film as a substrate of an organic electroluminescent element has been disclosed. As aforementioned transparent plastic film, for example, polyethylene telephthalate (hereafter, abbreviated as “PET”) of which oxygen permeation rate is relatively high has been used.
However, there has been a problem in that the gas barrier property of a film substrate such as a transparent plastic film is inferior to that of a glass substrate. For example, when such a substrate having an insufficient gas barrier property is used as a substrate of an organic photoelectric conversion element, water vapor or air may penetrates the substrate, resulting in the problem that the property tends to be degraded with time.
In order to overcome such a problem, a technique to provide a metal oxide thin layer on a film substrate to obtain a barrier film substrate has been known. As a barrier film used for a packaging material or for a liquid crystal display, a plastic film on which a silicon oxide or an aluminum oxide is vacuum evaporated has been known.
Instead of a vacuum evaporation method, a method to form a layer having a gas barrier property by applying a coating liquid containing polysilazane as a main component, followed by conducting a surface treatment has been known (refer t, for example, Patent Document 1). However, in none of these methods, the property as a gas barrier layer has been fully sufficient. Accordingly, a further improved gas barrier property, for example, a moisture permeating rate notably lower than 1×10−2 g/m2/day has been desired.
As a technique to further improve the gas barrier property, also known has been a method in which the aforementioned polysilazane layer and plasma chemical deposition method are used in combination (for example, refer to Patent Document 2). However, even in this method, aforementioned target of the gas bather property has not been attained.
A method to form a dense functional material exhibiting a peeling nature, an anti-scratching property, durability of luminance, permeability and a light blocking nature by using a plasma chemical deposition method employing a silazane compound as a raw material gas has been known. In the barrier film obtained by using this technique, there has been a possibility to generate particles of a size from submicron to micron, so called as “particles”, in the plasma space between the electrodes. The particles are reaction products of a raw material and have been a specific problem of a plasma chemical deposition method. There also has been a possibility that the particles adhere to the surface of the deposited layer to disturb formation of a uniform layer, whereby it has been possible to deteriorate the quality of the barrier film due to the defect caused by the particles.
As a means to disperse the defect and satisfy the demand of a high barrier property against moisture, a technique to attain a moisture permeability of less than 0.1 g/m2/day by using a laminate of an organic layer and an inorganic layer (for example, refer to Patent Document 3) has been disclosed. However, the organic-inorganic lamination type bather film disclosed in this document has had a problem that the bather nature is not fully enough.
Further, in this technique, it is necessary to form a layer under vacuum when the gas barrier layer is formed via a physical or a chemical deposition method, whereby it is necessary to reduce the atmospheric pressure in the film forming process, and to recover the normal atmospheric pressure after the barrier film formation, resulting in serious problems of increased equipment cost and production process.
Also, a technique to conduct a plasma chemical deposition method under an atmospheric pressure has been known. In this case, an adjusting process of the pressure can be avoided in the production process. However, in order to form a dense gas barrier film exhibiting a high barrier property, the accumulation rate is needed to suppress low. Accordingly, it has been difficult to attain an efficient productivity also in this case.
On the other hand, also known has been a gas barrier layer formation technique in which, after lamination of a partially alkali substituted polysilazane and a polysilazane, an oxidation treatment is conducted (for example, refer to Patent Document 4). However, only by the lamination of an alkyl substituted polysilazane layer and a polysilazane layer, the ability to relax the stress caused by bending the barrier film has not been enough, and the variation of barrier property due to heat or moisture, or after a long term storage has been large, whereby it has been difficult to maintain the barrier property in the early stage after the film production.
Instead of the aforementioned methods, the following technique has been known as a method to form a gas barrier film by conducting a surface treatment after a coating liquid containing polysilazane as a main component is applied (for example, refer to Patent Document 5). However, also in this technique, the function as a gas barrier layer of such as an organic EL element has been insufficient. Accordingly, further improvement in the gas barrier property, for example, a moisture permeability of notably lower than 1×10−2 g/m2/day, has been desired.